In a compression/expansion system for cooling a refrigerant gas, the gas is liquefied by compressing it, expanded through a nozzle or the like, during which it extracts heat from its environment, and it is then recirculated to a pump which re-compresses the gas for passage around the refrigerant gas/liquid circulation loop. Where the compression system is small, the liquid refrigerant can be used to lubricate the moving parts of the compression pump and its motor. However, where the system is large, typically handling heat extraction requirements of 10 Kwh or more, it is necessary to provide the compression pump and its motor with a separate lubrication system using a conventional lubrication oil. This can give rise to problems due to contamination of the lubrication oil by the refrigerant at those points in the refrigerant flow path where there is an interface with the lubrication oil. It is now a general health and safety requirement that all reasonable steps be taken in the design and manufacture of large scale refrigeration systems to isolate the refrigerant from the lubrication oil and purchasers will not buy systems where such steps have not been taken.
One such step has been the requirement that all joints in the refrigerant flow path be welded and not of the butting flange and gasket type of joint. Whilst welding the joints may minimize escape of refrigerant from the system at that point, it raises other problems for the manufacturer, the system installer and user and in servicing and repairing the system. Thus, it is commonplace in a refrigeration system to incorporate an oil cooler circuit in which lubrication oil from the refrigerant gas compressor is circulated through a cooler. This oil cooler circuit incorporates a by pass circuit and diverting valve mechanism so that some or all of the oil is passed through a secondary, by pass circuit and not through the cooler. By varying the proportion of oil which is directed to the by pass circuit as opposed to passing through the cooler, it is possible to control the cooling of the oil so as to maintain the optimum oil temperature. Thus, when the oil is at or near its design temperature, the majority of the lubrication oil is directed to the by pass circuit. However, when the oil is hot, for example when warm materials are placed in the cold room and must be cooled rapidly to the desired temperature thus requiring the compressor to work hard, the majority of the oil is directed through the cooler to reduce the temperature of the oil to within the desired design temperature range.
For convenience, the term refrigerant system of the above type will be used herein to denote refrigerant systems having the general features described above.
It is therefore commonplace to incorporate a control valve in the lubrication oil circuit which acts selectively to direct part or all of the flow of oil through the by pass circuit or the oil cooler. Such a valve typically comprises a thermally responsive mechanism placed in the oil flow path and actuating a multi port valve member in a three port valve body. Typically, this valve comprises a generally T shaped cast or machined stainless steel or other metal valve body having a fluid inlet at the base of the upright of the T and fluid flow outlets from the ends of the head of the T, one to the oil cooler and the other to the by pass circuit, with the valve mechanism located within the chamber formed in the valve body at the intersection of the upright and head of the T.
It will be appreciated that the valve mechanism may also act to mix hot oil from the compressor with varying amounts of oil which has passed through the cooler. In this case the valve acts as a mixer valve rather than as a diverting valve and the valve acts to regulate the flow of cooled oil from the cooler to be mixed with the warmer oil from the by pass circuit, the mixed oil flowing over the temperature responsive mechanism before flowing through the upright of the T back to the compressor pump.
However, it is necessary to have access to the operating components of the valve mechanism during construction and installation of the refrigeration system and for service and repair of the system once installed. Where all the pipe joints around the valve body are welded, as is desirable to reduce possible contamination of the lubrication oil by the refrigerant or escape of refrigerant gas from the lubricating oil through joints in the system, it would not be possible to gain access to the valve components located within the valve body. It is therefore customary to provided a flanged connection at the inlet to the upright of the T and to form a removable section in the pipework connected to that flanged connection. In this way, the removable section of the pipework can be removed to allow the installer or user to gain access to the interior of the T body of the valve and allow the operating components of the valve mechanism to be installed or removed from the valve body.
Such a design enables the internal components of the valve to be accessed, but introduces at least two flanged type of joints in the lubrication oil circuit, which is undesirable. However, no satisfactory alternative has been proposed and designers and operators in this field have accepted the presence of the flanged joints as an inevitable necessity in order to achieve access to the interior components of the valve mechanism.
It has been proposed in British Patent No. 1 382 225 to form a valve for use in mixing hot and cold water with a tubular member within which an obturator is moved axially by a temperature responsive mechanism to open and close apertures through the wall of the tubular member at each end thereof. However, an essential feature of the valve described is that is should be capable of being adjusted by a user so as to achieve a desired mixed water temperature. To this end, the temperature responsive mechanism is directly coupled to the obturator so that they are not capable of axial movement relative to one another. The coupled assembly is located upon an axially acting compression spring and the axial position of the assembly within the tubular member is adjusted by a screw mechanism acting in opposition to that spring. Such an assembly deliberately does not fix the temperature responsive mechanism axially with respect to the tubular member, but allows its axial position to vary so that the temperature of the delivered mixture of hot and cold water can be varied by a user. Such a valve is not suitable for use with the oil flow system for a compression pump for a refrigerant circuit where it is desired to maintain a substantially constant temperature in the lubricating oil passing through the compressor. Furthermore, in the valve design of BP 1 382 225, pressure fluctuations in the water passing through the valve could cause the temperature responsive mechanism to move axially against the bias of the compression spring. This will varying the position of the obturator and hence the temperature of the mixed water stream when no variation of temperature was required.
We have now devised a form of valve which reduces the above problems and avoids the need for flanged joints in the oil circuit pipework adjacent the valve. In the valve mechanism of the invention the internal components are located within a chamber within the valve body and can be inserted or removed through a sealable opening in a wall of the valve body. In this way the connections between the valve body and the remainder of the lubrication oil flow circuit pipework can be welded to minimise leakage, but access to the internal components of the valve can readily be achieved. Since the operating components of the valve are located within the valve body, the valve is compact and does not occupy excessive space, as would be the case if the operating components were mounted externally upon the valve body. Furthermore, if the operating components of the valve mechanism were mounted externally upon the valve body so that they were available for service or repair, this would require a complex and convoluted flow path for the lubrication oil through the valve mechanism and some form of sealing means for the flow of oil from within the valve body to the external operating components of the valve mechanism. We have found that by retaining the operating components within the valve body, the flow path can be simplified, thus minimising pressure drop and shear working heating of the lubrication oil.